3.4. Mechanical properties
Figs. 5–8 show the effect of ALK on the tensile, hardness
and resilience of the silica-filled NR vulcanisates.
It can be seen that M100 and M300 increased up to the maximum level (5.0 phr)
and then decreased with further increases in the ALK loading.
The results of the tensile strength and
hardness also exhibited a similar trend. According to Hertz
[22], and Ismail & Chia [23], the modulus or stiffness/
hardness and tensile properties are dependent only on the
degree of crosslinking. According to Ignatz-Hoover & To
[24], as the crosslink density of a rubber vulcanisates increases,
the elastic properties, such as tensile modulus,
hardness and tensile strength increase, whereas viscous
loss properties, such as hysteresis, decrease. Further increases
in the crosslink density will produce a vulcanisate
that tends towards brittle behaviour. Thus, at a higher
crosslink density, such elastic properties as mentioned
earlier begin to decrease.